PROCEEDINGS, Thirty-Eighth Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, February 11-13, 2013 SGP-TR-198 THE EXPLORATION AND UTILIZATION STATUS OF GEOTHERMAL RESOURCES AND FUTURE DEVELOPMENT IN TIANJIN, CHINA Ruan Chuanxia and Sun Yixuan Tianjin Geothermal Exploration and Development Designing Institute NO.29, Weiguodao, Hedong District, Tianjin, China Email: [email protected] China University of Geosciences, Beijing, 100083 NO.29 Xueyuan Road, Haidian District, Beijing, China Email: [email protected] years, the large-scale exploration and utilization of ABSTRACT this reservoir has resulted in a quick decline of water level. (Tian, G., Song, M., et al., 2011). This paper introduces geological structure features, exploration status, geothermal temperature characteristics and geothermal reservoirs in Tianjin. This paper further analyzes the questions in the process of development and utilization. The author provides the resolving methods for the porosity and karst reservoirs at the basis of finished research then states the future development and utilization of geothermal resources according to the present reservoir characteristics and the societal and the economy’s demand for geothermal resources in Tianjin. INTRODUCTION Tianjin is located in the northeast of the North China Plain, near Bohai Bay, at the lower reaches of Haihe River valley, with the Bohai Sea to the east and Figure 1: Location of Tianjin Yanshan Mountain to the north (Figure 1). There are over 15 districts and 3 counties under Tianjin’s 2 EXPLORATION STATUS OF TIANJIN jurisdiction that’s total area is 11,900 km . GEOTHERMAL RESOURCES Tianjin belongs to the warm temperature zone and has sub-humid continental monsoon climate that Geological structure makes all four seasons sharply distinguishable, and Tianjin’s geothermal field is located in a this results in a great difference in temperature and a sedimentary-fault basin in the north of the North wide variety of scenery throughout the year. The China Platform and is divided into a northern and a average temperature in a year is over 12.3°C with southern part by the Ninghe-Baodi fracture (Figure 200 days of a frost-free period. Winter temperatures 2). Quaternary strata cover most of the areas. The are low enough to make space heating a necessity. outcrop of base rock is limited to the north Mountain of Ji County. The geothermal resources in Tianjin are relatively abundant – so are its reserves – and the utilization of The northern part belongs to the secondary tectonic this rank number one in China. Tianjin’s geothermal unit. The southern part lies in the Bohai-Bay Basin. field is a typical low-temperature geothermal system 2 From west to east, the southern part constitutes three with an 8,700km distribution area where its tectonic units: they are the Jizhong depression, the occupation reaches 77% of the total Tianjin area. As Cangxian uplift, and the Huanghua depression, which the geothermal resource providing a substantial are all cut into numerous tectonic blocks by several amount of clean energy, Tianjin seeks to use it on east-west, north-west, and north-east trending space heating, potable water, agriculture, etc. Recent fractures. On the whole, the centre part is uplifted following: Quaternary, Neocene, Eocene, Mesozoic, Ordovician, Cambrian, Qingbaikou, and Jixian. The Tianjin geothermal reservoir consists of a fractured karst aquifer in the dolomite and limestone bedrock of the medium Proterozoic Jixiannian Wumishan group (Pt2W), the lower Paleozoic Cambrian group (PzH) and the Ordovician (PzO) group. Above that geothermal water is found in the porous clastic rocks of the Tertiary and Quaternary strata (Tianjin Regional Geological Records, 1992). Figure 2: The regional tectonics in Tianjin with the low-lying part in the east and west. The anticline structure is the main regional trend. The main fractures are the Tianjin fracture, the Cangdong fracture, the Baitangkouxi fracture, and the Haihe fracture. Most of the geothermal fields are located in the Cangxian uplift (Li Jun, Zhao Zijun et al., 2010). The area is fractured by several SW-NE and W-E trending faults, which control recharge conditions to geothermal systems. Figure 3 ： Map of Finished geothermal exploration area Exploration status The exploration of geothermal resources began in the Temperature characteristics nineteen-seventies. The large-scale exploration and The main factors affecting geothermal gradients are evaluation began in the nineteen-eighties. There are cap rock thickness, bedrock depth and form, 10 geothermal abnormal fields, including the structural form, faulting, lithology, and magma geothermal fields of Wanglanzhuang, Shanlingzi, activities, etc. Geothermal exploration has shown that Wanjiamatou, and so forth. the folding of the bedrock surface and faults are the main effectation on the distribution of geothermal The total exploration area is up to 3,000 km2, and the field. largest exploration depth is 4,000 m. The exploration of 8 geothermal fields had finished, which are Taking the geothermal gradients into consideration, Wanglanzhuang， Shanlingzi，Binhai, we regard the area in the north of Ninghe-baodi fault Wuqing, Panzhuang-lutai, Ninghe-hangu, as a low-valued region because of the shallow cap Wanjiamatou, and Zhouliangzhuang (Figure 3). The rock and the exposed bedrock. Cap rock has the total production of geothermal resources is 7,606.6× distribution characteristics of high value in the 104m3/a (more than 25 degree). The use of middle and low value on both sides. The quantities of geothermal energy is 1.30×1016 J/a that is equal to geothermal measured data prove that the concave and 4.43×105 t/a standard coal. convex constructs are of important influence on the distribution of geothermal field. There is a high value Drilling data shows that the exposed strata from the in the area of geothermal surface to the bottom of Cangxian uplift area are the gradient on the Cangxian uplift has and a low value on both sides of the depression (Figure 4). It is noteworthy that there are 7 geothermal abnormal areas on the Cangxian uplift which accounts for 84.4% in total geothermal abnormal areas (table 1). That distribution direction is consistent with the stretched direction of bedrock construct. The dense distribution area of geothermal gradient mainly lies around the fault area. The geothermal zone mainly stretches NNE direction, and secondly stretches EW and NWW. Geothermal reservoir There are two types of geothermal reservoirs in Tianjin. One is a closed clastic rock subsystem where geothermal water is present in pores. The other is a semi-open and semi-closed bedrock subsystem where the geothermal water is present in a karst formation. From the top to the bottom as shown in figure 5, the reservoirs are Minghuazheu reservoir (Nm), Guantaozu Figure 4 Distribution map of geothermal reservoir (Ng), Dongyingzu reservoir (Ed), Ordovician Gradient contour reservoir (O), Cambrian reservoir (Є) and Wumishan reservoir (Jxw) (Table 2 and Figure 5). The high value of Bedrock depth Control area Geothermal abnormal Construct location average geothermal (km2) area （m） gradient (℃/100m) Zhouliangzhuang Cangxian Uplift 880± 200 5.5 Wangcaozhuang convex Panzhuang Cangxian Uplift Panzhuang 1300± 600 6.9 convex Wangqingtuo Cangxian Uplift Dacheng 1400± 130 5 convex Qiaogu Huanghua depression 1700± 90 5.5 Ninghe convex Shanlingzi Cangxian Uplift 、 Da and 1200± 340 8.3 xiao dongzhuang convex Wanlanzhuang Cangxian Uplift Shuangyao 1000± 640 8.0 convex Wanjiamatou Cangxian Uplift 1000± 260 8.8 Xiaohanzhuang convex Tangguantun Cangxian Uplift Shuangyao 1200± 60 7.6 convex Shajingzi Huanghua depression 1500± 300 4.5 Beidagang convex Ninghe Huanghua depression 1700± 20 4.3 Construct belt Table 1, geothermal abnormal area in Tianjin Outflow Geothermal The top Flow rate quality Lithology temp. Hydro-chemistry reservoir Depth (m) (m3/h·m) assessment (°C ) Sandstone, HCO -Na Minghuazhen 300-600 40-70 0.76-5.43 3 Good silty sandstone SO4·Cl-Na Sandstone HCO -Na HCO ·Cl- Guantao 1200-2200 55-80 0.52-5.13 3 3 Good with gravel Na HCO -Na Cl·HCO - Dongying Sandstone 1900-2500 75-93 0.33-0.34 3 3 Good Na Highly Ordovician Limestone 882-3104 48-76 1.62-7.94 SO4·Cl-Na、 corrosive HCOHCO-Na 3HCO·Cl-Na·SO - Highly Cambrian Limestone 950-3734 70-80 2.11-3.13 3 3 4 Na corrosive HCO ·SO -Na Wumishan Sandstone dolomite 988-3000 79-105 6-12 3 4 Good Cl-Na Table 2: Main characteristics of geothermal reservoirs in Tianjin used for hot water and space heating. The geothermal wells of Guantaozu reservoir mainly lie in Huanghua depression and Jizhong depression where the water level drops, on average, respectively 1-6m/a and 1- 3m/a. The geothermal wells of Wuminshan reservoir used for hot water and space heating mainly lie in Cangxian uplift with the water level decreased 1-9m/a. Figure 5: Sketch of geothermal reservoir in Tianjin DEVELOPMENT AND UTILIZATION Development and utilization status of main reservoir Because of the simplification in utilization and the deficiency of heat exchanging when the geothermal water is pumped into the heating system, the heat efficiency decreases thereby prompting several serious questions such as why the pipelines corrode and why there is such a high magnitude of heat pollution. However, through the popularization of heat exchangers, frequency conversion, floor heating, automatic controlling techniques, and especially the Figure 6 Distribution map of geothermal wells success of reinjection tests in 1990s, the geothermal resources have been widely used in Tianjin for Reinjection Total Total economic planning. Along with the rapid growth of the Total Reinjec rate/ Reserv productionreinjection geothermal tion Production real estate market, the demands for geothermal energy oir rate rate wells well rate has increased enormously reflected in a rapid inreasing (×104m3) (×104m3) number of geothermal wells and the total area of space (％) heating. Currently, geothermal wells amount to 381, of Nm 90 3 442.32 0.89 0.20 which 313 are production wells and 68 are reinjection wells (Table 3 and Figure 6).